Various methods have heretofore been proposed for the purpose of prolonging the effective life of physiologically active substances, where a physiologically active substance is contained in a carrier of a polymeric substance. In particular, a natural polymeric substance such as a cellulose or a starch is proposed as being preferable as a carrier in such case in a form wherein the physiologically active substance-containing carrier is used as found in nature and therefore must be safe. Such natural polymeric substances include a chitin of an amino-polysaccharide. In this connection, U.S. Pat. No. 3,911,098, corresponding to Japanese Patent Application (OPI) No. 123815/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) discloses a drug-releasing instrument, where a drug is incorporated in a chitin solution and the resulting mixture is shaped to form a shaped body which may slowly release the effective ingredient of the incorporated drug. This prior art technique, however, has some problems, in that the chitin component used therein is a water-soluble chitin derivative, and therefore, when said drug-releasing instrument is used in the presence of water, the carrier itself is dissolved and the effect of the physiologically active substance contained therein does not last for a long period of time.
The present inventors have conducted extensive studies to overcome the above-mentioned problem and to obtain a biolytic drug-releasing body comprising a water-insoluble chitin as a carrier, and as a result, previously proposed a method where a physiologically active substance is incorporated in a swelled body of a water-insoluble chitin, as described in U.S. application Ser. No. 637,191, filed Feb. 8, 1984, now U.S. Pat. No. 4,704,268, corresponding to Japanese Patent Application No. 145428/83). However, this prior art process still involves a problem in that a physiologically active substance can generally not be incorporated in the carrier at a desirably high concentration.
A shaped chitin body containing a physiologically active substance at a high concentration is disclosed in Chem. Pharm. Bull., Vol. 29, pp. 3067-3069 (1981), where a chitin is dissolved in hexafluoro-2-propanol, and a drug is added thereto in an amount of 200 wt. % with respect to the amount of the chitin, and thereafter the solvent is evaporated to obtain drug-containing chitin-tablets. However, the solvent used in this method is extremely specific and expensive, and is highly toxic. In addition, the retention percentage of the physiologically active substance in the formed tablets is 25% or less, and the duration for releasing the active substance is almost within 24 hours.
U.S. Pat. No. 4,059,457 discloses a method for preparing a shaped chitin body, wherein a chitin is dissolved in a lithium chloride-containing dimethylacetamide solution or in a lithium chloride-containing N-methylpyrrolidone solution, and the resulting chitin-dope is coagulated with a coagulant to obtain a shaped chitin body. However, there is no disclosure in U.S. Pat. No. 4,059,457 with respect to a method where a physiologically active substance is incorporated in a chitin-dope.